New radar tracks fowl flight
As the sun sets on the salt marshes and barrier islands of the Virginia Coast Reserve, Sarah Mabey can be found sitting in a windowless steel cargo container. She's staring into a weather-radar screen ... bird-watching.
Birds have been showing up on radar scopes since World War II, often baffling early operators. But Dr. Mabey and her fellow scientists are using the technology for a far more serious purpose.
Some 60 to 80 percent of birds die during their first year, a huge number of them during migration. To give young birds a fighting chance, the researchers are trying to discover where they take off, what land they use for emergency stops, and where they go for longer rest and refueling.
"We're trying to protect these birds during the most dynamic and perhaps vulnerable part of their annual cycle," says Mabey, a postdoctoral researcher at North Carolina State University in Raleigh. "Birds don't occupy just one space. They get blown off course by weather, they go with the wind. So they end up in different places. So we hope radar will help us get a handle on what are those most important places."
There's one problem. Today's standard Doppler radar is limited in what it can tell about rain - or birds. On radar, birds look like raindrops except they sometimes flow up instead of down - in big blocks of atmosphere the size of one cubic kilometer. That's a rough measure to pinpoint which land surface the birds on radar just took off from.
But a new opportunity came last spring for Mabey when fellow researcher Barry Truitt, a scientist with the Nature Conservancy, learned that the National Aeronautics and Space Administration was looking for the ideal location to test its new high-resolution polarimetric radar.
Sensing an opportunity, Mr. Truitt suggested a partnership. The Conservancy, which owns the 38,000-acre Virginia Coast Reserve, would supply NASA with a prime location to watch storms developing off the coast.
In return, perhaps NASA would let scientists study bird behavior with the radar when it wasn't being used to track storms.
"They said we could use the radar, but that it had filters on it to screen out the birds," Truitt recalls. "I said, 'Well, could you see birds with it if you turn the filters off?' They said, 'Sure.' "
As one of only a handful worldwide, the NASA Polarimetric Radar or NPOL can peer into the atmosphere with roughly 2,000 times more precision than standard Doppler radar.
In addition, NPOL calculates objects as they move in both vertical as well as horizontal space. It may one day be possible to calculate whether the radar is seeing a goose or a sparrow.
For now, researchers are using NPOL to pinpoint the landscape critical to bird migration. That will allow the Nature Conservancy and others to identify and purchase more important migratory rest stops.
The idea is to use NPOL to set conservation priorities based on scientific assessment of birds' actual behavior and needs - not simply what is most convenient to preserve or what humans just guess will protect them.
With the landscape so fragmented by development along the eastern seaboard between New York and Washington, D.C., the issue of land preservation for birds is coming to a head, Truitt and others say. And because land is costly to purchase and set aside for nature, identifying precisely which land is most essential to birds during migration may be a key to their survival.
As soon as next month, Mabey expects to unveil research that may show some surprising results, including areas of central Virginia long thought to be of little value to birds, that are in fact quite valuable.
That won't come as a surprise to Truitt, who knows firsthand that birds find rest in many unusual places. While he was surf fishing off the Virginia coast, he spotted a bird flying directly at him from the open ocean. It landed on the shirttail of his jacket - and fell sleep.
"I put it on my shoulder and it stayed there an hour before it finally woke up and flew to a thicket on the dune," he recalls. "That yellow-billed cuckoo had been blown far out to sea by a storm and had finally made it back. It was so tired, I guess I just looked like the nearest tree."
Which is why rest areas for birds are so critical, he says. Without them such birds might not be able to recoup and continue migrating.
"These birds are not using the eastern shore because it has such great habitat," Truitt says. "It's because the eastern winds bring them here. And that makes it doubly important to protect the few remaining areas that can support them."